A prior art storage structure and a prior art vehicle for use with the storage structure are illustrated in FIGS. 1 and 2, respectively. The storage structure 3 comprises a vehicle or robot 1 which is arranged to move on dedicated supporting rails 13 and to receive a storage bin 2 from a storage column 8 within a bin storage grid 15. The storage structure 3 includes a plurality of such vehicles 1 and a dedicated bin lift device 50, the latter being arranged to receive a storage bin 2 from the vehicle 1 at the top level of the bin storing grid 15 and to convey the storage bin 2 down in a vertical direction to a delivery station 60.
When a particular storage bin (denoted a “target bin”) on a lower level within the storage structure is to be fetched, a vehicle 1 is controlled to pick up the upper bin from the stack of bins located vertically above the target bin, and then the vehicle 1 is controlled to unload and store this bin on a selected location on the upper level of the storage grid. This process may then be repeated until the target bin has become the upper bin in the vertical stack of bins. Then the target bin is fetched by the vehicle 1 and carried by the vehicle 1 to the bin lift device 50.
This system and operational method has certain disadvantages. First, the intermediate storage of bins on top of the upper level of the storage grid occupies area, resulting in obstructions for other vehicles that are intended to move as freely as possible on the top of the upper level of the storage grid. Second, a substantial amount of time is spent on the loading and unloading of bins associated with the intermediate storage. This in turn contributes to significant delays in the overall pick up time used to obtain a desired target bin.
WO-2013/167907 relates to a storage system suitable for storing multiple product lines in an automated warehouse environment. A first handling device is capable of lifting a plurality of containers from a stack in a single operation, and a second handling device is capable of lifting a single container and moving the container laterally.
This system has certain disadvantages. First, the first handling device, lifting a plurality of containers, causes a potentially tall stack of containers to be stored in the first handling device. This results in instability and risk for overturning, in particularly during acceleration/movement of the first handling device. Second, a special multi-bin handling device is needed for the lifting of a plurality of containers. The multi-bin handling device is different from the single-bin handling device used to retain the single container. The use of dedicated handling devices for various purposes results in a complex system.
An object of the present invention is to solve, or at least substantially alleviate, the above-described disadvantages of the prior art storage structures and methods.